Why didn’t the Hi Ad design ever get used by MLW? What was the advantage of the Dofasco truck, especially when the Hi Ad was only a few years old? Dofasco was a foundry, which also cast GM Blomberg, Flexicoil, and HT-C. Where then did the truck design on the big 6 axle MLW units originate? Did either CP, or CN mechanical department put in 2 cents, or did MLW come up with it? I was on a CP photo site, and the earlier C630M units, with the Dofasco trucks came while Alco Schenectady was still in business.

The "Dofasco" truck had a much shorter wheelbase, so might have been better on sharp curves. (CP and CN through the Rockies aren't exactly Shinkansen alignments...) I think this may have been the primary selling point. It also at least LOOKS simpler, so it may have been a bit cheaper.The Alco 3-axle Hi-Ad was, I think, a bit better at high speeds (and I think I have seen it referred to as a "High Speed Truck"), and I think gave a smoother ride on straight or mildly curved track. The Western Australian iron ore railroads had both C-636 (with the Alco truck) and M-636 (with the Dofasco), both built under license in Oz. These are very well-engineered railways: I don't think they have as sharp curves as the western Canadian lines. My impression is that the operators preferred the C-636.It's not going to happen tonight, but I think I may be able to find an old issue of an Australian railfan magazine with an article about these truck designs (comments above are largely my vague recollections of things said therein)-- will post again with more detail when/if I find.

I can't find a truck diagram for 6 axle Hi-Ads, but the 4 axle trucks were not zero weight transfer trucks, so the 6 axles might not have been as well, which would mean the Dofascos would have better adhesion on starting.

What constitutes a zero weight transfer truck? I assumed it was that the bolster connection was at the same height as the wheel axles? That was true of the Alco 2 axle Hi-Ad truck, according to the Steinbrenner book. If so, then it was indeed a ZWT design. If it is something different, what makes it so?

According to Steinbrenner the 3 axle Hi-Ad truck also had its bolster connection at the wheel axle height, so it was the same as the 4 axle truck in that regard. As for the Dofasco truck, Steinbrenner states that (as asserted above) it was developed to allow for sharper curves. The Hi-Ad had a wheelbase of 13 ft 7 inches (compared to the 12 ft 6 in of the Trimount), while the Dofasco truck's wheelbase was only 11 ft 2 in. The Dofasco truck was a bolsterless truck; it was attached to the carbody using rubber/metal sandwich assemblies. It was tested by the CN against other truck designs and found to be superior, and thus became standard equipment on MLW locomotives for the three largest Canadian railroads.

Re: "The Dofasco truck was a bolsterless truck; it was attached to the carbody using rubber/metal sandwich assemblies. It was tested by the CN against other truck designs and found to be superior, and thus became standard equipment on MLW locomotives for the three largest Canadian railroads."And I think it was claimed in an article in the same Australian railfan magazine ("Motive Power," and I couldn't find the relevant issue in the basement when I looked the other night-- I don't think I would have "de-accessioned" it, and will look again) that the qualities of the Dofasco truck surprised the engineers at General Electric's Erie plant when the first M630/C630 were traded in on C40-8 or C40-8M, and this is part of why GE abandoned the FB3 truck they had used since 1966 in favour of the "roller blades" truck on the Dash-9 series.

Could GE have dusted off the Dofasco truck, or were the ever increasing size of new units made the concentrated load on roadbed and bridges too heavy, due to the short wheelbase? Maybe the rights to the design weren’t available?

Apparently, you’re saying that the Dofasco design was something MLW developed independent of their bosses in Schenectady?

I have looked at a 2 axle HiAd, which was on a M&E unit. I don’t recall how the bolster height compared, but mechanically they look like a Blomberg. The only difference is the large coil springs replace the leaf springs.

What constitutes a zero weight transfer truck? I assumed it was that the bolster connection was at the same height as the wheel axles? That was true of the Alco 2 axle Hi-Ad truck, according to the Steinbrenner book. If so, then it was indeed a ZWT design. If it is something different, what makes it so?

I remember making that assumption many years ago and I was told that's not what constitutes a ZWT truck, because it doesn't account for the height difference between the bolster and the forces generated at the wheel tread.

Whether a truck counts as "ZWT" depends less on the aesthetics and more on the way the design transfers forces to the frame. In the case of the MLW 2-axle ZWT truck, my understanding is that the rubber pads visible above the side frame are NOT the only (or even the main) suspension components. There is another set of angled rubber pads hidden behind the frame, set at an angle and located much closer to track level. The EMD HT-B truck used on the GP40X uses a similar design, except with the pads outboard of the frame. The result is that the forces that would normally cause weight transfer off the leading axle are cancelled out by the suspension.

Regarding the Dofasco/MLW 3-axle truck, it incorporated several features not present in the ALCO Hi-Ad design, such as having the motors all facing the same direction and using a stiff bolsterless secondary suspension. These features were adopted by EMD and GE in their current truck designs - in fact, GE essentially copied the Dofasco rubber pad secondary suspension as-is for the Hi-Ad truck used in Dash-9 and later units.

This is from memory (I still haven't been able to find the issue of the Australian magazine(*) with the article about the Hi-Ad truck). The "Dofasco" truck(whatever its official name is, this is in common usage so I'll call it that) has a very short wheelbase for a three-axle truck. This was, for CN, a feature, not a bug (one of th corporate ancestors of CN, the Canadian Northern, was very much a low-budget operation, and CN has a lot of track whose alignment, by the standard of CP or the big U.S. railroads, is pretty curvy). It does, however, lead to weight concentration, and I think GE felt that a longer-wheelbase truck would go over better with most customers.The "roller blades" truck was developed, I think, by or at least with the assistance of GE's European partner, Krupp. As the very visible spring hangers show, the primary suspension of the roller blades truck is differently arranged from that of the Dofasco truck, and I assume that GE felt that this was preferable to just trying to make a lengthened version of the Dofasco truck.

(*) The magazine was (is?) called "Motive Power". The article was one of a series (others discuss EMD and Alco prime movers) by Peter Clark, run as sort of a column with the title "My Personal View." There are still parts of my basement where my copy might be, but if anyone else has a run of "Motive Power" from the 1990s and early 2000s...

Found it! (Parts of my collection of old railfan and model railroading magazines are systematically organized. "Motive Power" by and large went into the other part.)

So. The article, "The Design of Locomotive Bogies," by Peter Clark, is in "Motive Power," issue number 4, of February 1999, pp. 4-7. The magazine is still in business (I found their WWWebsite by searching "motive power magazine"), and has a number of back issues still available, but none this far back. I'm not sure of the legalities as to scanning the whole thing and posting it here: moderator please advise me?

Clark discusses several bogie ("truck" in American) designs: the GE FB-3, the Dofasco, the Alco 3-axle "Hi-AD," and cast and fabricated versions of the GE "Roller Blades." All have seen use in Australia, particularly on Alco and GE designed locomotives for the Western Australian iron ore railroads. These are (mostly) heavily engineered heavy haul lines, and since being built in the 1960s have been operated with North American style high horsepower 6-axle locomotives, of types differing only slightly (typical change: more radiator capacity for operation in a very hot desert) from domestic U.S. and Canadian models.

GE's FB-3 was introduced (domestically) in 1966. Clark says "While it did not actually use any EMD patent designs, it was clearly similar in concept to the Flexicoil [except for] us[ing] rubber/metal sandwich construction secondary springs, while EMD were still using coils at that time. The rubber/metal sandwich was very stiff vertically, confining most movement to the primary springs, but was relatively soft laterally, absorbing shocks that would have been transmitted to the locomotive frame."

The Alco truck (used on C636 and some C630) was introduced in 1967. According to Clark, in its initial advertising Alco called it a "High Speed" truck, switching to "Hi-Ad" later. (AH comment: I think the Alco two-axle Hi-Ad, as used on most C430, one order of LIRR C420, and one each of C415 and T6 for the MCRR, was legitimately described as a High Adhesion truck. Perhaps Alco advertising … confused the attributes of the two truck designs?)

Clark says of it: "It had large widely spaced coil springs, and the bolster was connected to the frame with low level traction rods. The coil springs were mounted on rubber pads, giving more lateral freedom. This produced an excellent high speed bogie, that rode very well, and its adhesion performance was on a par with its contemporaries, but in no way was it a 'High Adhesion' bogie."

I'll post further summaries and excerpts later, about the Dofasco and GE designs. For tonight I'll finish with a relevant comparison between units with the Alco and Dofasco trucks. Mt. Newman Mining, one of the Western Australian iron ore railroads, had a fleet of C636 and M636 locomotives (all, I think, built by licensees in Australia). Their railroad is very well engineered, with "relatively gentle" curves, and they specified the Alco truck "even on Montreal designed locomotives." Eventually they were forced to accept the Dofasco truck on their later units "but they never liked it." According to Clark, most of the units with Alco trucks were rebuilt with GE power (AH comment: these units have a unique, Australia-only cab, but otherwise look, to an American, like weird Alco-GE hybrids: C636 trucks and fuel tanks below the frame, but C36-7 or C40-8 long hoods above!), but the newer units with Dofasco trucks were scrapped sold or donated to museums. And: "Six GE locomotives were built new with the floating bolster bogie, but they are not as popular as the Alco bogied rebuilds."

I read that the ALCO Hi-AD trucks did rode very well in Australia with long welded rails and well maintained road bed. In the US, especially on IC, where the tracks were jointed and poorly maintained, the Hi-AD has a tendency to bounce and shake. Steve Lee wrote a piece in Trains magazine about his bad experience working on C636 on IC, one of the units even bounced itself off the rails.

Most trucks today uses a combination of coil springs and rubber damper (either the rubber/metal sandwitches on the floating bolster and GE Hi Ad trucks or the donut shaped rubber rings one might find on many European/Asian passenger vehicles) From what I understand coil springs are effective in absorbing low frequency shocks where rubber components smoothes out the high frequency shocks.

I bet Bogieman/Dave should be the best person to comment on this topic.